LUCIANO BERIO's "Coro," a complex musical tapestry for 40 voices and 40 musical instruments that receives Washington premiere tonight with the Cleveland Orchestra, is utterly unlike any other lengthy symhonic setting of poetry.

First, there is the floor plan -- which is the key to the Italian composer's aesthetic concept. It is unique in that the orchestra is placed on individual platforms arranged in a semicircle across the stage, while the chorus of 10 each of sopranos, contraltos, tenors and basses is broken up so that each singer stands near one of the platforms.

In "Coro" (which means "Chorus") each singer is paired with an instrument of roughly comparable timbre and range. The sopranos, for instance, are paired off with four flutes, oboe, E-flat clarinet, trumpet and three violins. The pairs may either perform together, against each other or alone (the opening is a Sioux Indian song sung in English by a soprano accompanied by piano). The texts are from two sources -- folk poetry in various languages and cries for relief from repression by poet Pablo Nureda.

"Coro" consists of 31 continuous episodes and lasts about an hour. It will be the only work on tonight's program, which will be conducted by Lorin Maazel.

Berio came to write this work, which was composed about five years ago -- at the same time that he was writing a new cello composition for Rostropovich -- from parallel lines of thought thought: one musical, the other social. Talking about "Coro" recently, Berio said, "Strangely enough, this work was written when the blood in the streets of Italy came out. I have always been sensitive to this problem, this change. In 'Nones,' which is taken from 'The Ninth Hour,' by W. H. Auden, you have the very hour when Christ died -- the ultimate moment. This is the theme, if you want the acute awareness of things at a tragic moment."

Berio quotes these lines from Auden: What we know is not possible Though time after time foretold . . . comes to pass Before we realize it: We are surprised At the ease and speed of our deed And uneasy: it is barely three, Mid afternoon, yet the blood Of our sacrifice is already Dry on the grass; we are not prepared For silence so sudden and so soon . . .

"Also this was a tribute to Neruda and what he represented. Neruda was practically murdered -- not physically, but spiritually -- they broke his heart. If you want, it is an invitation to be aware of the violence of the times, Fascist violence."

Neruda, the Chilean poet who was awarded the Nobel Prize for literature in 1971, died in 1973. Berio uses fragments of Neruda poems written between 1933 and 1947. A refrain which runs throughout the work and returns at its close, is the line "Venid a ver la sangre por las calles" ("Come and see the blood in the streets").

Berio has musical reasons for the shape and sound of "Coro" that match the social concerns out of which it was born. "I think it is common in all my life that I have been interested in making the two things converge: voices and instruments. In 'Sinfonia' and 'Labyrinth,' etc., I have always been interested acoustically to create a unity. So this is not an idea that came suddenly. Here the novelty is that I bring together many different things, a multitude of things. In previous works there was a state of unity. Here it goes back from African techniques to very complex situations, so that the range is much wider.

"In central Africa a friend of mine found the people making a polyphony of 42 voices! Very complex. But you know, it is very important to me that in this work I tried to compose on different levels of understanding. There is not just one level of perceiving the work. There is every way of listening: you may listen to a Mozart symphony only in terms of melody. That's poor, but it's there, you can do it. Of course the deeper you go, the more you are rewarded. So here there is a simpler level of perception, then it is more complex. It's one of the great privileges of music that there is a certain complexity of perception: the 'Grosse Fuge' [of Beethoven] is complex. But then you can generate simpler levels.

"So 'Coro' is a sounding together, instruments and voices. It's a chorus of many different aspects, so the arrangement is important because they are sitting at very special places. You must see the soloists in the chorus. There are 40 marriages, 40 couples. Every voice has an instrument. It is a very visual piece. There is a duet between the first bass and the first trombone; a duet for the French horn and the first tenor; for the fourth tenor and the cello. You must see it."

At the center of the orchestra is the piano. At times the huge score sounds almost like a piano concerto. "I use the piano because it is a kind of universal instrument," Berio explains. "It is a kind of leader. Sometimes the piano becomes the skeleton within the music, especially when I develop African techniques."

In his "Points on a Curve to Find written shortly before "Coro," Berio, writing for solo piano and 22 instruments, used the piano homophonically, making a virtue of an inherent limitation in the instrument, the extremely rapid decay of its notes.

Berio discussed the difficulties and problems of "Coro": "It is very taxing for the chorus because they are soloists most of the time. Also it is psychologically something new for them. I didn't want to have too much range of foreign language, so where there are some African or Iranian texts, I translate them into German.It is all in French, Spanish, Italian, English or German.

"Also there is a kind of phonetic material derived from the test because at times the articulation is such that they could not possibly sing words. I could just as well have used the telephone book.

"For the conductor [and Berio him-self conducted the work for its DGG recording, 2531 270], the problem is one of balance -- balance in voices, the identity and articulation of voices. Also meters, harmony and melodic elements. Some of this is transparent, very clear. It sounds better in a hall. One of the most rewarding things for me in rehearsing for the first time was because of the distribution. You have a completely different geography in the orchestra. Flute there, tuba here, trumpet there. And the sound is fantastic. When you record this, you completely destroy it. It's amazing how fresh it is to hear the different distribution of sounds -- double bass, first violins, trumpets, horns, and to separate everybody.

"And gradually, toward the end, the two texts come together -- the blood in the life of love and work, and the blood in the streets."